Industrial technique

ABSTRACT

A heat exchanger that transfers heat generated within a nuclear reactor to a secondary coolant has a support system that accommodates thermal expansion and contraction as well as seismic forces through an arrangement of trunnions and trunnion bearings. The trunnions that are secured to the outer edge of the top tube sheet are limited to movement in a longitudinal direction. The bottom tube sheet trunnions confine the heat exchanger to movement in only one transverse direction. Turning movements produced at the trunnions because of these motions are relieved through lubricated rotation blocks in the trunnion bearings.

United States Patent Anderson et al.

[ Mar. 26, 1974 INDUSTRIAL TECHNIQUE Inventors: Gerald G. Anderson; Ronald C.

Hutto, both of Lynchburg, Va.

Assignee: The Babcock & Wilcox Company,

New York, NY.

Filed: Dec. 21, 1971 Appl. No.: 210,476

[52] U.S. Cl. 165/68, 308/6 [51] Int. Cl F281 9/00 [58] Field of Search 165/68, 81, 86, 162, 47;

[56] References Cited UNITED STATES PATENTS 3,236,295 2/1966 Yurko 165/81 3,587,727 6/1971 Tokumitsu 165/68 3,622,211 11/1971 Mitton 308/6 Primary Examinercharles Sukalo Attorney, Agent, or Firm-J. M. Maguire, Esq.; J. P. Sinnott, Esq.

[ 5 7] ABSTRACT A heat exchanger that transfers heat generated within a nuclear reactor to a secondary coolant has a support system that accommodates thermal expansion and contraction as well as seismic forces through an arrangement of trunnions and trunnion bearings. The trunnions that are secured to the outer edge of the top tube sheet are limited to movement in a longitudinal direction. The bottom tube sheet trunnions confine the heat exchanger to movement in only one transverse direction Turning movements produced at the trunnions because of these motions are relieved through lubricated rotation blocks in the trunnion bearings.

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INDUSTRIAL TECHNIQUE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to heat transfer equipment and more particularly to improvements in the heat exchanger support structure for a nuclear power system, and the like.

2. Description of the Prior Art Transferring heat from one fluid to another is a common industrial process. Usually, the apparatus for effecting a transfer of this character is referred to as an heat exchanger. In a typical device of this sort, a hot fluid enters an inlet head. The fluid then flows through a bundle of tubes that are anchored to the inlet head tube sheet. After completing a circuit through these tubes, the fluid discharges into an outlet head, which also has a discharge tube sheet in order to secure the terminal ends of the tubes in the bundle.

A secondary coolant may be introduced into the heat exchanger through an opening in a wrapper or shroud that forms the enclosure for the tube bundle. The secondary fluid passes over the bank of tubes and, after absorbing heat from the fluid within the tubes is discharged through an outlet in the heat exchanger.

Chemical processing plants, refineries, nuclear power generation stations and any number of other commercial and industrial enterprises require this sort of equipment. Because of the large fluid volumes with which many of these installations must cope, the associated heat exchangers often are of large size.

A nuclear power station, for example, may require four heat exchangers, each about 12 feet in diameter and more than 70 feet long. These heat exchangers will convert the secondary coolant into steam in order to drive the electrical generation equipment in the power plant. The heat that produces steam in the secondary coolant is, of course, extracted from the hot, pressurized reactor coolant water flowing through the tube bank. Inasmuch as the temperatures involved in this process frequently exceed 2,000 F, structural provisions must be made for the effects of thermal expansion and contraction.

The difficult problem of accommodating these thermal effects in such large equipment is further aggravated by the need to compensate for a postulated Loss of Coolant Accident." For the purpose of reactor safety analysis, it is assumed that almost all of the primary coolant suddenly drains from the reactor core. This condition, it is believed, will be reflected in an abrupt and radical change in the structural temperatures of the heat exchangers. A concomitant thermal contraction of these heat exchangers might occur so swiftly that they would actually produce a damaging impact on the surrounding structures.

Earthquakes and other events which may cause dynamic loading are also believed to be capable of producing similar forces that might have the same destructive potential as this proposed loss of coolant accident. Massive and costly ring girders have been used to support the steam generators, to counter the anticipated forces, and. to cope with changes in the points of heat exchanger load application that tend to vary with thermal or seismic conditions. Hydraulic suppressors also have been used for this same purpose. Not only do these suppressors require continued inspection and maintainence, but also the reliability of these devices is not entirely certain.

Accordingly, a need exists to accommodate these forces in a more efficient manner.

SUMMARY OF THE INVENTION The present invention to a large extent satisfies these needs through an arrangement of trunnions and trunnion bearings that restrain the movement of the heat exchanger. Trunnions, for example, are secured to the external surfaces of the inlet and discharge tube sheets. The set of trunnions that protrude from the discharge tube sheet rest in bearings that are free to move in a transverse line that is perpendicular to the longitudinal axis of the heat exchanger. The set of trunnions secured to the outer surface of the inlet tube sheet, moreover, are seated in trunnion bearings that restrict the heat exchanger to movement in the direction of the longitudinal axis.

Confining the heat exchanger to movement in only two directions necessarily produces a twistingor rotation at the trunnions. For example, a transverse movement at the lower tube sheet will produce a turning moment that causes at least some of the inlet tube sheet trunnions to rotate. Rotation blocks in the trunnion bearings afford a stress-free accommodation that enables the trunnions to turn with relative freedom and thereby prevent stresses from developing in the structure.

In accordance with a feature of the invention, the trunnions are received in apertures that are formed in the rotation blocks. Bearing plates engage the sides of the individual blocks in order to give freedom of movement in one axial direction and restrict motion in the other directions. Thus, the trunnion rotation blocks move with the associated trunnions in response to the over-all motion of the heat exchanger that has been permitted at each of the respective sets of trunnion bearings. In this manner stresses caused by torque forces are relieved in the rotation blocks and axial forces are borne by the bearing plates that engage the blocks.

The trunnion bearings are received on structural steel frameworks. These frameworks distribute the heat exchanger load to appropriate bearing surfaces, e.g. the secondary radiation shielding in a nuclear power plant. This system for load distribution establishes a basis for a more efficient support structure because the points of heat exchanger load application are fixed and thus do not shift in response to changes in seismic or heat exchanger thermal conditions.

Accordingly, the invention, and particularly the movable rotation block in the trunnion bearing overcome the need for massive ring girders and bothersome hydraulic suppressors that have characterized the prior art.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation of a typical heat exchanger embodying principles of the invention;

FIG. 2 is a plan view in full section of the heat exchanger shown in FIG. 1 taken along the line 22 and looking in the direction of the arrows with trunnion bearings and a typical support framework added for descriptive purposes;

FIG. 3 is a plan view in full section of the heat exchanger shown in FIG. 1 taken along the line 3-3 and looking in the direction of the arrows, also with trunnion bearings and a typical support framework added to the figure;

FIG. 4 is a detail view in side elevation of a typical trunnion structure associated with the inlet tube sheet;

and

FIG. 5 is a detail view in side elevation of a typical trunnion structure associated with the discharge tube sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENT For a more complete appreciation of the invention, FIG. 1 shows a typical heat exchanger for use in a nuclear power system that has a pressurized water reactor coolant. The heat exchanger 10 includes an inlet conduit 11 that channels the hot pressurized water from the nuclear reactor core (not shown) to an hemispherical inlet head 12. The inlet head 12 terminates in a flat inlet tube sheet 13 that secures the inlet ends of the individual tubes (not shown) in a bank or bundle within the heat exchanger.

A wrapper 14 encloses the entire active volume of the heat exchanger 10 in order to establish a space in which a secondary coolant contacts the tubes in the bank that carries the pressurized water from the inlet head 12 to an hemispherical discharge head 15. The discharge end of these tubes, moreover, are anchored in a flat discharge head tube sheet 16.

It should be noted, in connection with large heat exchangers of the type under consideration, that the tube sheets may accommodate as many as l5,000 tubes, each tube having an outside diameter of five-eighths of an inch. Tube sheets for installations of this sort often are on the order of 24 inches thick.

Returning to FIG. 1, the primary coolant or pressurized water is pumped from the discharge head 15 through a conduit 17 for recirculation back through the reactor. Heat carried by the primary coolant is absorbed in a secondary coolant that flows into the heat exchanger 10 through a main feedwater inlet 20. T. S. Sprague US. Pat. No. 3,447,509 granted on June 3, 1969 for Once-Through Vapor Generator" describes in more complete detail a typical feedwater circulation through the heat exchanger 10. The feedwater enters the heat exchanger and absorbs heat from the pressurized water. The absorbed heat causes the feedwater to rise into steam and flow out of the heat exchanger 10 through a steam outlet 21.

A heat exchanger of the sort under consideration might weigh as much as 600 tons and be subject to temperatures that range from ordinary atmospheric to 2,000 F and more. Clearly, in a massive structure of this character, small thermally initiated heat exchanger movements of not more than a few inches can produce substantial impact forces, if the temperature change is sufficiently swift.

In accordance with the invention, these structural support difficulties are alleviated to a large extent by securing trunnions 22, 23, and 24 to the inlet head tube sheet 13. A trunnion 25, also secured to the inlet tube sheet 13, is out of the plane of the FIG. 1 drawing. The trunnion 25, however, is shown in plan view in FIG. 2. All four of the trunnions preferably are bolted to the outside surface of the tube sheet 13. They are, moreover, spaced at intervals from each others.

The trunnions 22, 23, 24, and 25 that are secured to the inlet head tube sheet 13 assist in accommodating the expansion of the heat exchanger 10 in the direction of a longitudinal heat exchanger axis 26, as described subsequently in more complete detail. Movements of the heat exchanger 10 in a direction that is transverse or perpendicular to the longitudinal axis 26 are carried through trunnions 27, 30, and 31. A trunnion 32 is not shown in FIG. 1 because it is out of the plane of the drawing. This trunnion nevertheless is shown in plan view in FIG. 3. All of the trunnions 27, 30, 31 and 32 are preferably secured by bolts to the exterior surface of the discharge head tube sheet 16.

Turning now to FIG. 2, a plan view is shown of an illustrative trunnion bearing and structural support system for accommodating longitudinal movements of the heat exchanger 10. A structural steel framework 33 is anchored into the reinforced concrete in a secondary radiation shield (not shown) that is provided for the reactor system. The framework 33 distributes the entire heat exchanger load in all conditions of seismic and thermal stress to specific bearing points in the radiation shield. In this manner a more efficient and less expensive construction is possible because the shield does not have to be designed to cope with the shifting points of load application that have characterized prior heat exchanger supports.

Illustratively, the framework 33 is a welded structure that is assembled from wide flange beams. Beams 34 and 35 in the framework 33, for instance, ultimately support the trunnion 23 that is attached to the inlet head tube sheet 13. The trunnion 23 has a cylindrical protruding member or pin 36 that is received in a rotation block 37 which has a cylindrical central aperture 40 for engaging the pin 36. To enable the trunnion pin 36 to rotate freely within the block 37, a very precise fit at the local maximum heat exchanger temperature is provided between the surface of the aperture 40 and the mating cylindrical surface of the pin 36. To reduce friction, the carbon steels from which the pin 36 and the block 37 are formed should have different hardnesses. At lower temperatures, of course, the tit is less tight. A flat retainer plate 41 is bolted to the end of the trunnion pin 36 that is not secured to the inlet tube sheet 13. The retainer plate 41 has a flange that extends beyond the maximum diameter of the pin 36 in order to engage the external surface of the rotation block 37. It should be noted, moreover, that the length of the pin 36 is slightly greater than the corresponding thickness of the rotation block 37 to establish a clearance 42 that will permit the heat exchanger 10 to expand in a radial direction.

In FIG. 4, the bearing for the trunnion 23 is shown. This trunnion bearing enables the rotation block 37 to slide in the direction of the heat exchangers longitudinal axis 26. To provide this restraint on the motion of the block 37, two longitudinally disposed bearing plates 43 and 44 engage the longitudinal sides of the rotation block 37. High temperature grease filled grooves can be formed in the plates 43 and 44 in order to reduce friction forces and lubricate the vertical movement of the rotation block 37. Alternatively, the plates 43 and 44 can be machined from a low friction material, e.g. Lubrite.

The plates 43 and 44 are attached to edges on respective web members 45 and 46 by means of countersunk bolts 47. The opposing edges of the web members that support the bearing plates 43 and 44, respectively, establish a gap that matches the transverse width of the generally square-shaped rotation block. The longitudinal extent of the web members 45 and 46 is, however, significantly greater than the corresponding longitudinal dimension of the rotation block 37. This clearance enables the block 37 to move in a longitudinal direction in response to shifts in the size and position of the heat exchanger with respect to the axis 26, while restraining the trunnion 23 from all significant movement in a transverse direction. Thus, the block 37 prevents torsion rotation from being developed as a consequence of pin translation, while enabling the trunnion to move with relative ease in the longitudinal direction.

The web members 45 and 46 are welded to transversely disposed and abutting flanges 48 and 49. The flanges 48 and 49 bridge the gap or clearance that was established between the two webs 45 and 46 to accommodate the rotation block 37. These flanges and webs abut and are fastened to a pair of longitudinal butt straps 50 and 51, the strap 50 being secured to the end of the web 45 and the strap 51 being secured to the end of the web 46. The butt straps 50 and 51 are, in turn, secured through bolts 52 to corresponding and matching butt straps 53 and 54, respectively, on the opposing ends of the beams 34 and 35. This assembly enables the trunnion 23, and the associated trunnion bearing to become an integral part of the framework 33. Shims 55 and 56 respectively are inserted between the opposing faces of the flanges 50 and 53 and the flanges 51 and 54 in order to compensate for minor inaccuracies and misalignments. All of the trunnion assemblies that are associated with the inlet tube sheet 13 (FIG. 1) are of similar construction.

Turning now to H0. 3, trunnion bearings 57, 60, 61, and 62 associated with the discharge head tube sheet 16 distribute a proportionate share of the load imposed by the heat exchanger to the secondary shield system through a structural steel framework 63. As hereinbefore mentioned, the trunnion system that is secured to the discharge head tube sheet 16 only accommodates movement in a line that is perpendicular to the longitudinal axis of the heat exchanger. This accommodation, moreover, is limited to motion in the direction of transverse axis 64. Accordingly, the trunnions 31 and'27, which are in diametrical alignment with each other on the discharge tube sheet 16, are supported in the bearings 57 and 61 for sliding motion in directions that are parallel to the transverse axis 64. More specifically, the trunnion 31 transfers a proportionate share of the heat exchanger 10' load to the trunnion bearing 61 through a rotation block 65 which receives a cylindrical trunnion portion or pin 67. As described in connection with the trunnion 23 (FIG. 2), the trunnion 31 in FlG. 3 terminates in a retainer plate 70 that has a flange which overlaps the external surface of the rotation block 65.

A clearance 71 is established between a shoulder 72 on the trunnion 31 and the inner surface of the rotation block 65 to provide for the thermal expansion of the heat exchanger 16% in a radial direction.

Turning now to FIG. 5, it can be seen that two parallel sides 73 and 74 of the generally square block 65 are in sliding engagement with matching surfaces on lubricated bearing plates 76 and 77 respectively. The bearing plates 76 and 77 are secured to transversely disposed flanges 86 and 81 respectively with counter-sunk bolts 82. The flanges 8t) and 81, moreover, are joined to longitudinally positioned web members 83 and 84. The web members, however, are spaced from each other to form an oblong rectangular aperture, the longest dimension of which is parallel to the planes of the flanges and 61. This longest aperture dimension is greater than the corresponding dimension of the block 65 to establish clearances 90 and 91. These clearances enable the block 65 to move in a transverse direction, e.g. in the direction of the axis 64 shown in FIG. 3. Because the spacing between the opposing surfaces of the bearing plates 76 and 77 is equal to the width of the block 65 between the sliding edges 73 and 74, the flanges 80 and 81 restrain the block 65 and the associated trunnion 31 from movement in the direction of the heat exchangers longitudinal axis.

The trunnion bearing assembly is secured to the steel framework 63 by means of longitudinally disposed butt straps 88 and 89. These butt straps 88 and 89 are bolted, or otherwise acceptably secured to cognate butt straps 85 and 86 that form a part of the support framework 63. Shims 87 can be interposed between the joined pairs of butt straps to provide an adjustment for minor misalignments, and the like. To further support the heat exchanger, a longitudinally disposed beam can be secured to the flange 81, if required.

As hereinbefore mentioned, the movement of the heat exchanger inthe transverse plane is restricted to the axis 64 that is shown in FIG. 3. Accordingly, the trunnions 30 and 32 and the associated trunnion bearings 60 and 62 are provided with some clearance to accommodate the heat exchangers thermal expansion and contraction in a radial direction and motion along the transverse axis 64. To prevent transverse movement in a direction that is perpendicular to the axis 64, rotation blocks in the trunnion bearings 60 and 62 are rigidly engaged within respective frameworks 68 and 69. These rotation blocks, immobile in transverse and longitudinal directions, thus only relieve rotational forces induced by torques that develop within the heat exchanger system.

It is preferable to maintain the entire heat exchanger system at a stable temperature throughout its operational life. Of course, installation, repair, and maintenance, as well as potential seismic and loss of coolant problems necessarily require that the heat exchanger should be capable of cycling through a complete temperature range several times. Clearances that will permit about three inches of longitudinal movement and two inches of movement along the transverse axis 64 (PEG. 3) appear to be sufficient for heat exchangers of the general size under consideration.

Thus, in accordance with the terms of the invention, impact loads due to seismic disturbances, loss of coolant accidents, and the like, apply compressive stresses to the individual beams in the framework 63 (FIG. 3). This is a preferred structural condition. The trunnion system and the associated frameworks, moreover, dissipate these forces at specific load-bearing points in the secondary shielding, as distinguished from prior systems, in which the points of load application tended to shift in response to changes in physical conditions. The rotation blocks provide still a further feature of the invention. These blocks enable the trunnion pins to move in predetermined axial directions, while accommodating heat exchanger turning moments. The number of trunnions required for each installation can vary from the eight shown in the illustrative embodiment, in accordance with specific requirements.

We claim:

1. A system for supporting a heat exchanger having a longitudinal axis comprising trunnion means secured to one longitudinal end of the heat exchanger to enable the heat exchanger to move on an axis in a plane that is transverse to the longitudinal axis of the heat exchanger and restraining the heat exchanger from movement on other transverse axes, and further trunnion means secured to another longitudinal end of the heat exchanger to enable the heat exchanger to move on the longitudinal axis, all of said trunnion means having clearances to accommodate thermal expansion and contraction of the heat exchanger in transverse directions.

2. A system according to claim 1 wherein all of said trunnion means further comprise pins for dissipating torsion forces that develop in response to said axial movements of the heat exchanger.

3. A system according to claim 2 wherein all of said trunnion means further comprise rotation blocks each individual to a respective one of said pins, said rotation blocks enabling said pins to move pivotally and on said transverse and longitudinal axes. 

1. A system for supporting a heat exchanger having a longitudinal axis comprising trunnion means secured to one longitudinal end of the heat exchanger to enable the heat exchanger to move on an axis in a plane that is transverse to the longitudinal axis of the heat exchanger and restraining the heat exchanger from movement on other transverse axes, and further trunnion means secured to another longitudinal end of the heat exchanger to enable the heat exchanger to move on the longitudinal axis, all of said trunnion means having clearances to accommodate thermal expansion and contraction of the heat exchanger in transverse directions.
 2. A system according to claim 1 wherein all of said trunnion means further comprise pins for dissipating torsion forces that develop in response to said axial movements of the heat exchanger.
 3. A system according to claim 2 wherein all of said trunnion means further comprise rotation blocks each individual to a respective one of said pins, said rotation blocks enabling said pins to move pivotally and on said transverse and longitudinal axes. 